The present inventions relate in general to semiconductor technology, and in particular to power semiconductor devices and methods of manufacturing the same.
Several types of power semiconductor devices, such as transistors and diodes, comprise vertical devices. A vertical device generally comprises a mesa structure formed in a semiconductor epitaxial layer of a semiconductor substrate, where the mesa is defined by one or more trenches disposed in the epitaxial layer and around the mesa. A controllable current flows from the mesa's top to the mesa's bottom, in a direction that is generally perpendicular (e.g., vertical) to the surfaces of the epitaxial layer and semiconductor substrate. The vertical device typically has an ON-state where the current flows through the mesa with a low amount of electrical resistance, and an OFF-state where the current flow is substantially suppressed, except for a very small leakage current. In the OFF-state, the voltage that can be sustained through the mesa while suppressing current flow can be very high, such as in the range of several tens of volts. However, due to various processes occurring in the semiconductor material, such as carrier avalanche, the ability to suppress the current flow in the OFF-state fails at a certain level of voltage, which is often called the breakdown voltage.
There is a continuing need to improve the reliability and performance of trench-shield power semiconductor devices. This includes increasing the value of the aforementioned breakdown voltage, and improving the electrical characteristics of the devices formed in the mesas.